Aqueous dispersions of spontaneously cross-linking polymers and copolymers are produced by the polymerization of acrylic or methacrylic amides in which the amide groups are substituted by methylol or methylol ether groups. The polymers and copolymers which are obtained can be converted under the action of heat or acid catalysis, or both, into cross-linked insoluble polymers. In most cases, such cross-linking occurs spontaneously leading to gelatinized products.
Aqueous solution polymerization of N-methylolacrylamide (NMA) normally results in a highly gelled, water-insoluble mass which is characteristic of the cross-linking between the highly reactive methylolhydroxyls of the N-methylolacrylamide monomer. In fact, normal solution polymerization of N-methylolacrylamide in aqueous media is virtually impossible due to the ease of condensation between the highly reactive methylols. Additionally, N-methylolacrylamide polymerizes extremely quickly into very high molecular weight polymers. Prior to the instant invention it was very difficult to produce low molecular weight poly(N-methylolacrylamide).
U.S. Pat. No. 3,178,385 discloses stable aqueous dispersions of spontaneously cross-linking polymers. The copolymers are produced by the copolymerization of a mixture of monomers comprising (1) derivatives of Mannich bases of acrylic and methacrylic amides and (2) methylol compounds of acrylic and methacrylic amides. Polyethoxylated emulsifiers are listed as suitable emulsifiers for the copolymerization reaction.
U.S. Pat. No. 3,288,740 discloses a process for the manufacture of stable copolymers of N-methylol substituted amides of acrylic acid by emulsion polymerization of the monomers in an aqueous medium wherein the polymerization is performed in the presence of a minor proportion of a water soluble alkaline earth metal salt of an alpha, beta-ethylenically unsaturated monocarboxylic acid. Stable dispersions of the copolymers are reported to result because premature cross-linking and gelatinization is avoided by this process which is carried out in the usual manner in water with the use of nonionic emulsifiers such as polyethoxylated compounds.
U.S. Pat. No. 3,300,439 discloses alkylolated acrylamide interpolymers having at least some of the amido hydrogen atoms replace by an alkylol group etherified with a polyhydric alcohol. The interpolymer ether produced in the presence of a polyhydric alcohol retains a reactive group, namely the remaining hydroxyl functionality of the polyhydric alcohol, for cross-linking cure upon baking.
U.S. Pat. No. 3,732,184 discloses a two stage polymerization of monoethylenic monomers. The monomers must include reactive monomers, such as N-methylolacrylamide, capable of thermosetting cure. Polyethoxylated octyl phenol was used as a nonionic emulsifing agent to produce a polymer latex containing a thermosetting polymer which has the capacity to cure to greater insolubility by the two stage emulsion polymerization method.
U.S. Pat. No. 4,044,197 discloses a thermally self cross-linkable ethylene/vinyl acetate copolymer containing from 2 to 10% by weight of a copolymerizable compound containing an N-methylol group. Suitable dispersing agents are the emulsifiers generally used in the emulsion polymerization including polyethylene oxide containing emulsifiers.
F. E. Bailey, Jr. et al, Journal of Polymer Science: Part A, Vol. 2, 845-851 (1964) discuss the molecular association of poly(ethylene oxide) and poly(acrylic acid) in aqueous solution.
H. Kamogawa and T. Sekiya, Journal of the Chemical Society of Japan, Industrial Chemistry Section, 63 (9), 1631-1635, September 1960, discuss the problems of aqueous polymerization of N-methylolacrylamide by K.sub.2 S.sub.2 O.sub.8 and by H.sub.2 O.sub.2, and of copolymerization with acrylamide.
N. G. Gaylord in "Matrix Polymerization and The Effects of Polymers on Grafting" which was published in Block and Graft Copolymers, J. J. Burke and V. Weiss, Eds. Syracuse University Press, 1973, p 19-50, discusses the effect of polymers on the structure and properties of monomers polymerized in their presence, a phenomenon known as "matrix polymerization."
Nevertheless, there exists a need for the ability to polymerize N-methylolacrylamide without attendant gelatinization.
There is a need for a method for producing ungelled poly(N-methylolacrylamide) of low molecular weights.
Further there is a need for a method for controlling the polymerization of N-methylolacrylamide and selectively generating a poly(N-methylolacrylamide) molecule of a desired length.